Free adult health calculator
BMI Calculator
Calculate your body mass index using your height and weight, see the corresponding adult BMI category and view the weight range associated with a BMI of 18.5 to less than 25.
- Metric and imperial measurements
- Instant result explanation
- Your information stays on your device
Enter your measurements
This calculator uses the standard adult BMI formula and is intended for adults aged 20 years and older.
Your BMI result will appear here
Enter your height and weight to calculate your BMI, adult BMI category and corresponding reference weight range.
Your calculated body mass index
BMI is a screening measure and should be considered alongside other health information.
Three simple steps
How to Use the BMI Calculator
You only need your current height and weight. The calculator applies the standard adult BMI formula and explains what the result means in general terms.
Choose Your Measurement System
Select Metric if you know your height in centimetres and weight in kilograms. Select Imperial to use feet, inches and pounds.
Enter Your Height and Weight
Use your current measurements and check that they have been entered in the correct fields. Decimal measurements are accepted where appropriate.
Review the Complete Result
Select “Calculate My BMI” to see your BMI, adult category, category range and the BMI reference weight range for your height.
Understanding the calculation
What Is BMI and How Is It Calculated?
Body mass index, usually shortened to BMI, compares a person’s weight with the square of their height. It provides a quick screening estimate of weight relative to height.
What the BMI Number Represents
BMI converts height and weight into a single numerical result. For adults aged 20 years and older, that result can then be compared with standard adult BMI categories.
Because height is squared in the formula, the calculation adjusts weight in relation to overall body size rather than looking at weight alone.
BMI is most useful as a general screening measure . It does not directly measure body fat or distinguish fat mass from muscle, bone and other body tissues.
Metric BMI Formula
If height is entered in centimetres, it must first be divided by 100 to convert it to metres.
Weight: 75 kg
Height: 175 cm, or 1.75 m
Calculation: 75 ÷ (1.75 × 1.75)
Imperial BMI Formula
Feet must first be converted to inches. Multiply the number of feet by 12 and then add any additional inches.
Weight: 165 lb
Height: 5 ft 9 in, or 69 in
Calculation: (703 × 165) ÷ (69 × 69)
Reading your result
Understanding Adult BMI Categories
For adults aged 20 years and older, BMI results are grouped into standard screening categories. The obesity category is further divided into three classes.
Adult BMI Category Table
| BMI category | BMI range | General interpretation |
|---|---|---|
| Underweight | Less than 18.5 | Below the standard adult healthy-weight BMI range. |
| Healthy Weight | 18.5 to <25 | Within the standard adult healthy-weight BMI range. |
| Overweight | 25 to <30 | Above the standard adult healthy-weight BMI range. |
| Class 1 Obesity | 30 to <35 | The first of the three standard adult obesity classes. |
| Class 2 Obesity | 35 to <40 | The second of the three standard adult obesity classes. |
| Class 3 Obesity | 40 or greater | Also described in the CDC classification as severe obesity. |
Strengths and limitations
How Accurate Is BMI?
BMI accurately performs the mathematical comparison of weight with height. Its limitation is that this simple calculation cannot describe every part of an individual’s health or body composition.
What BMI Can Do
- Compare body weight with height using a standard formula
- Place an adult result into a recognised screening category
- Provide a quick starting point for a broader health conversation
- Help monitor broad changes in weight relative to height over time
What BMI Cannot Do
- Directly measure body fat percentage
- Separate fat mass from muscle, bone and other lean tissue
- Show where body fat is located
- Diagnose a disease or provide a complete picture of health
Factors That Add Context to a BMI Result
The same BMI number may need different interpretation depending on the person and the other information available.
Muscle Mass
A person with substantial muscle mass may have a higher BMI even when the additional weight is not primarily body fat.
Fat Distribution
BMI does not indicate where fat is carried. Waist-related measurements can provide different information about body shape and central fat distribution.
Medical History
Existing health conditions, family history and changes in weight over time may all affect how a result is interpreted.
Other Health Markers
Blood pressure, glucose, cholesterol, physical examination findings and health behaviours may provide additional context.
Remember: a BMI result should not be used on its own to make medical, dietary or treatment decisions. A qualified health professional can consider the result alongside your individual circumstances.
Appropriate use
When Adult BMI Needs Extra Context
The standard adult BMI formula can calculate a number whenever height and weight are entered, but that does not mean the adult categories are suitable or equally informative in every situation.
Children and Teenagers
People aged 2–19 should be assessed using BMI-for-age percentiles that account for age and sex. The fixed adult categories shown by this calculator should not be used to classify a child’s or teenager’s weight.
Adult calculator not designed for this groupPregnancy
Weight changes are an expected part of pregnancy, so a BMI calculated from current pregnancy weight should not be used in the same way as a standard adult result. Pregnancy-related weight questions should be discussed with a qualified maternity or healthcare professional.
Specialist pregnancy guidance neededPeople With Substantial Muscle Mass
Muscle contributes to body weight. Because BMI cannot distinguish muscle from body fat, a highly muscular person may receive a result in a higher category even when the additional weight is largely lean tissue.
Result requires body-composition contextMedical or Physical Circumstances
Conditions or circumstances that substantially affect body weight, fluid levels, muscle mass, body structure or the accuracy of height measurements may make a standard BMI result less representative.
Individual assessment may be more usefulQuestions to Ask Before Interpreting the Number
- Is this calculator designed for my age and circumstances?
- Could muscle mass or a recent body change affect the result?
- Has my weight changed unexpectedly or rapidly?
- What do my waist measurement and other health markers show?
- Do I have symptoms, medical conditions or concerns that need professional assessment?
Using your result responsibly
What to Do After Calculating Your BMI
A BMI result can provide useful context, but it should not automatically lead to a major diet, exercise or weight-related decision. Use the result as a starting point for a broader assessment.
Check Your Entries
Confirm that your height, weight and measurement system were entered correctly. A unit error can substantially change the result.
Read the Full Explanation
Review the category, category range, reference weight range and limitations rather than focusing only on the BMI number.
Add Personal Context
Consider weight trends, body composition, waist measurement, medical history and other available health information.
Decide Whether to Seek Advice
If the result causes concern or appears alongside symptoms, unexplained weight change or a health condition, professional guidance may be appropriate.
Consider the Broader Picture
Important: BMI and related calculators provide estimates for general information. They should not be used alone to diagnose a condition, set a personal treatment target or replace qualified healthcare advice.
Putting the number in context
What Your BMI Result May Mean for Your Health
BMI can help identify whether weight is relatively low or high for height. It may contribute to a broader assessment of health risk, but the number does not determine your health by itself.
If Your BMI Is Below the Healthy-Weight Range
A lower BMI may simply reflect a naturally smaller build, but it can sometimes appear alongside inadequate nutrition, unintentional weight loss or an underlying health issue. The BMI result alone cannot identify the cause.
If Your BMI Is Within the Healthy-Weight Range
This means your weight falls within the standard adult BMI range of 18.5 to less than 25 for your height. It remains important to consider other factors such as activity, sleep, nutrition, blood pressure and medical history.
If Your BMI Is Above the Healthy-Weight Range
Higher BMI categories are associated at a population level with increased risk for conditions such as high blood pressure, high cholesterol, type 2 diabetes, cardiovascular disease, sleep apnoea and joint problems. An individual BMI result does not show whether any of these conditions are present.
Other Information That Adds Context
Medical safety notice: this information is general and educational. It cannot diagnose an illness, determine your personal ideal weight or replace advice from a qualified health professional. Please read our Medical Disclaimer.
Common questions
BMI Calculator Frequently Asked Questions
Find concise answers about adult BMI ranges, calculation methods, accuracy and appropriate use.
What is considered a healthy BMI for an adult?
The standard healthy-weight BMI range for adults aged 20 years and older is 18.5 to less than 25. BMI is a screening measure, so a result within this range does not provide a complete assessment of health.
How is BMI calculated?
In metric units, BMI is calculated by dividing weight in kilograms by height in metres squared. In imperial units, weight in pounds is divided by height in inches squared and the result is multiplied by 703.
Does BMI measure body fat?
No. BMI does not directly measure body fat. It uses only height and weight and cannot distinguish fat from muscle, bone and other lean tissue. It also does not show where body fat is located.
Are adult BMI categories different for men and women?
Standard adult BMI categories use the same numerical thresholds regardless of sex. However, body composition can differ between individuals, which is one reason BMI should be considered with other health information.
Is BMI accurate for muscular people and athletes?
BMI can calculate weight relative to height, but it cannot determine whether that weight comes from fat or muscle. People with substantial muscle mass may therefore receive a higher BMI category that does not fully represent their body composition.
Can this BMI calculator be used for children and teenagers?
No. This calculator uses fixed categories intended for adults aged 20 years and older. Children and teenagers aged 2–19 require BMI-for-age percentiles that account for age and sex.
Can I use this BMI calculator during pregnancy?
A BMI calculated from current pregnancy weight should not be interpreted like a standard adult BMI result because weight changes are expected during pregnancy. Pregnancy-related weight questions should be discussed with a qualified maternity or healthcare professional.
Why might another BMI calculator give a slightly different result?
Small differences can result from rounding height, weight, unit conversions or the final BMI number. Check that both calculators use the same measurements and units before comparing the results.
Does a healthy BMI mean that I am healthy?
Not necessarily. BMI is only one screening measure. Medical history, body composition, blood pressure, laboratory results, physical activity, nutrition, sleep and other factors can all contribute to a more complete picture of health.
Should I change my diet or exercise routine based on BMI alone?
No. A single BMI result should not be used by itself to make major diet, exercise or treatment decisions. Consider your broader health circumstances and seek qualified professional guidance when appropriate.
Evidence and transparency
BMI Sources and Quality Standards
The formula, adult categories and interpretation guidance used on this page are based on established public-health references. We also explain the calculator’s assumptions and limitations.
Primary BMI References
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CDC — Adult BMI Calculator
Official adult BMI calculator and introductory guidance for adults aged 20 years and older.
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CDC — Adult BMI Categories
Adult BMI category thresholds, including the three standard obesity classes.
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CDC — About Body Mass Index
Explanation of BMI as a screening measure, including strengths, limitations and individual-health context.
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CDC — BMI Frequently Asked Questions
Guidance about BMI calculation, interpretation, body fat, muscular builds and child versus adult assessment.
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NIH/NHLBI — Calculate Your BMI
National Heart, Lung, and Blood Institute BMI calculator and adult category information.
External references open in a new browser tab. Source pages may be revised by their publishers as guidance changes.
Medical safety notice: EverythingCalculated.com provides general educational information and calculated estimates. It does not diagnose medical conditions, determine an individual ideal weight or replace care from a qualified health professional. Please read our full Medical Disclaimer.
Ready to Calculate or Review Your BMI?
Return to the calculator to check another measurement, or explore the complete Health and Wellness collection for more free calculators and explanatory tools.
- Free to use
- Metric and imperial units
- Methods and limitations explained
BMI results are general screening estimates and are not medical diagnoses or personalised weight recommendations. See our Medical Disclaimer.